1. Field of the Invention
The present invention relates to a wavelength converted light emitting apparatus, and more particularly to a light emitting apparatus and manufacturing method thereof for producing specific colors of light, such as white light, by converting the wavelength of a portion of the light to be emitted, by making use of phosphors.
2. Description of the Related Art
Semiconductor light emitting diodes are devices having a great potential for miniaturization and good light emission efficiency, and thus they have been utilized as optical sources of various display apparatuses and optical communication equipment. Further, as semiconductor light emitting diodes, which produce blue or ultraviolet light of a short wavelength, have been commercialized in recent years, the semiconductor light emitting diodes can serve to produce white light through the combination of blue, red and green light.
Generally, respective semiconductor light emitting diodes have a feature of emitting single color of light having a predetermined wavelength. Therefore, two typical methods have been used in order to realize emission of white light. One typical method is for integrating two or more kinds of light emitting diodes into a single package, and the other method is for converting a portion of the light emitted from a blue or ultraviolet light emitting device by making use of phosphor, so as to produce white light. Conventionally, the latter method is widely utilized since it is advantageous in view of miniaturization of products.
FIG. 1a illustrates a wavelength converted light emitting diode using phosphor. More particularly, the light emitting diode shown in FIG. 1a may be a light emitting diode 10 adapted to mainly emit white light.
Referring to FIG. 1a, the white light emitting diode 10 comprises a gallium nitride (GaN) based light emitting structure including an n-type GaN clad layer 12, a single quantum well (SQW) or multiple quantum well (MQW) active layer 13, and a p-type GaN clad layer 14, which are successively stacked on a sapphire substrate 11 in multiple layers. This GaN based light emitting structure further includes a first bonding electrode 16a formed on the upper surface of the n-type GaN clad layer 12, and a second electrode 16b formed on the upper surface of the p-type GaN clad layer 14. For the formation of these electrodes, the clad layers are processed by mesa-etching. The white light emitting diode 10 further comprises a phosphor layer 20 provided at the overall upper surface thereof. As used herein, “phosphor” refers to a wavelength convertible material for producing white light. That is, in a state wherein the active layer 13 of the white light emitting diode 10 emits blue or ultraviolet light, most of the emitted blue or ultraviolet light is converted into long wavelength light while passing through the phosphor layer 20. Then, the long wavelength light is combined with the remaining unconverted portion or differently converted portion of the blue or ultraviolet light, thereby allowing desired white light to be finally produced.
Since the conventional white light emitting diode 10 shown in FIG. 1a is manufactured in such a manner that, after the phosphor layer 20 is formed on the overall upper surface of a wafer, which is formed with a plurality of the light emitting diodes, and then the wafer is cut so as to form a plurality of individual chips, the phosphor layer 20 exists only on the upper surface of the white light emitting diode 10.
In this case, upward light A emitted from the upper surface of the white light emitting diode 10 passes through the phosphor layer 20 serving to stimulate the light emitted from the active layer 13 into white light, while lateral light B emitted from the side surface of the white light emitting diode 10 does not pass the phosphor layer 20, thereby being inevitably emitted as the original blue or ultraviolet light itself. As can be well noted from this fact, the light emitting diode 10 shown in FIG. 1a, which is formed only on the upper surface thereof with the phosphor layer 20 due to its manufacturing manner, has a problem in that it is very disadvantageous for the emission of appropriate white light.
As another example of conventional light emitting diodes, FIG. 1b illustrates the structure of a white light emitting diode using a phosphor material in accordance with the prior art. In FIG. 1b, the phosphor material is added at a package level of the light emitting diode.
Referring to FIG. 1b, the white light emitting diode package, designated as reference numeral 50, comprises a cup shaped package structure 42, which is mounted with a substrate 44 having a first electrode formed thereon. That is, the first electrode is formed on the substrate 44 within the cup shaped package structure 42. On the first electrode is mounted an ultraviolet or blue light emitting diode 30. This light emitting diode 30 is connected to an electrode pattern provided in the cup shaped package structure 42, that is, to a second electrode formed on the substrate 44 through wires 45.
Inside the package structure 42 mounted with the light emitting diode 30 is formed a molded portion 40, which is made of a luminescent material including appropriate phosphor. The phosphor for use in the molded portion 40, for example, may be a yttrium-aluminum-garnet-based luminescent material. Such a luminescent material is obtained by mixing a hardener with an unhardened epoxy resin powder as a main material, thereby producing epoxy slurry. As the epoxy slurry is provided inside the package structure by using a dispensing method, the phosphor molded portion 40 is constructed. Since the phosphor existing inside the molded portion 40 takes the form of scattered phosphor particles, a portion of the light emitted from the light emitting diode collides with the scattered phosphor particles, thereby undergoing wavelength conversion, while the remaining portion of the light directly passes through the molded portion 40 without conversion of wavelength. The combination of the wavelength converted light and other light can appear white to the human eye. The formation method of the phosphor as stated above is further applicable to form the phosphor layer 20 as shown in FIG. 1a. 
The phosphor molded portion 40 or the phosphor layer 20, however, results in a non-uniformity in spatial distribution of the phosphor particles scattered therein, and especially, in case of the structure shown in FIG. 1a, the phosphor layer 20 cannot be formed throughout the light emitting surface of the light emitting diode as stated above. Therefore, there is a problem in that it is very difficult to obtain desired colors of light from the overall light emitting surface of the light emitting diode. This problem is a big roadblock to commercialization of the wavelength converted light emitting diodes using phosphors.
Therefore, there has been a requirement of a wavelength converted light emitting diode structure capable of overcoming the above problems in the art.